High-efficiency extraction of aluminum from low-grade kaolin via a novel low-temperature activation method for the preparation of poly-aluminum-ferric-sulfate coagulant

Abstract

A facile hydrometallurgical method was proposed for high-efficiency extraction of aluminum at low activation temperature from low-grade kaolin involving sulfuric acid assisted activation followed by water leaching. After the slurry mixture of low-grade kaolin and sulfuric acid solution was stirred at 25 °C for 3 h and further heated at 150 °C for 2 h, the optimal extraction efficiencies of Al (98.8%) and Fe (98.1%) were achieved via water leaching at room temperature. The activation mechanism was proposed via investigating the intermediates during the activation process. It was found that the low activation temperature and the high extraction efficiencies result from the intercalation of sulfuric acid. The poly-aluminum-ferric-sulfate (PAFS) coagulant was further obtained from the leachate, and its coagulation performance was evaluated by jar tests. It was found that the PAFS is highly effective under acid conditions, and shows the highest removal efficiency of 93.7% for Direct Blue 2B with a dosage of 140 mg/L. Furthermore, the leaching residue was also utilized to prepare silica for rubber compounding ingredients to make full use of the silicon in low-grade kaolin, and simultaneously reduce the discharge of waste. Moreover, the corresponding scale-up experiments and the extended experiments showed that the Al extraction efficiencies of the diasporic bauxite and the spent fluid catalytic cracking catalyst reach 95.4% and 97.2%, respectively via the proposed method. This work provides a new highly efficient Al extraction strategy from low-grade kaolin and other similar ores and wastes containing rich Al element to prepare Al–Fe coagulant.